1. Field of the Invention
The present invention is directed to a pulse sequence for operating a magnetic resonance system for monitoring the chronological flow within a vessel.
2. Description of the Prior Art
A number of different methods are known for executing a flow measurement in a vessel using the phenomena of nuclear magnetic resonance. These known techniques have in common the selective excitation of a slice of an examination subject which is disposed perpendicularly relative to the flow direction. During the on-time of the slice selection gradient, an additional phase is impressed on displaced spins, so that the resulting signals can be evaluated to obtain information about the flow.
It is also possible to generate an image of the examination subject in which the flow can be seen by applying further gradients. Such a method is disclosed in "MR Angiography with Gradient Motion Refocusing," Laub et al., Journal of Computer Assisted Tomography, Vol. 10, No. 5, pages 715-722, Sept./Oct. 1986. In this method, as in standard imaging methods, three orthogonal gradients are used, namely a slice selection gradient, a read gradient and a phase coding gradient. The phase coding gradient is forwarded from scan to scan as in the standard spin warp method, so that a full topical resolution is achieved. Using this method, however, relatively long examination times are required to display the chronological course of the flow.
The portrayal of the chronological course of a flow is of significant diagnostic value. In conventional methods, this course can only be displayed by ECG triggering which, however, is time-consuming, and is not as useful a diagnostic tool as a real-time display.